On-demand type ink jet printers are used in, for example, computer systems, electric calculators, cash registers, automated teller machines (ATM), facsimile apparatuses and the like. In an ink jet printer, ink droplets are ejected or jetted to a recording sheet to form letters, figures, or pictures thereon in accordance with a predetermined dot matrix. That is, typical ink jet printing systems consists basically of forming a letter or a figure on a recording medium by ejecting droplets through at least one small nozzle in a preselected arrangement. These ink droplets can be formed by, for example, electrostatic charging, application of thermal energy or application of mechanical energy. One known device for supplying mechanical energy is the piezoelectric device.
It is advantageous that an ink jet printer have the following characteristics for use as a high quality printer in the aforementioned devices:
1. The ink must be consistently discharged by the ink jet printer through each selected nozzle without any clogging during prolong continuous operation. A clogged nozzle can result in misformed or unformed characters. PA1 2. The printer must be free of meandering flying of ink drops. In other words, the ink drops must be printed in their respective desired locations. Otherwise, characters may be distorted or misformed. PA1 3. The ink must dry immediately after printing to prevent smudging and smearing. PA1 4. The printer must consume a minimal amount of electrical energy. PA1 5. The printer must have a small size. PA1 6. The printer must be inexpensive to maintain and manufacture.
It has been proposed to provide an ink jet or recording head, including the supply passage ways and the ink tank, composed of a plastic material. A plastic ink head can be fabricated by means of, for example, molding and welding of performed plastic pieces. These processes are well known for inexpensively and reliable fabricating such recording heads. Additionally, plastic possesses superior chemical resistance. In view of the above, plastic is a very desirable material for use as an ink jet head.
However, conventional techniques do not provide for a plastic ink jet head which can print images and characters with high quality. This can be explained as follows. Plastics generally do not have characteristics of affinity for water or good water characteristics. In other words, plastics can hardly be wetted by water or ink having water soluble dye. As such, passage ways fabricated in the ink plastic head are hardly wetted with the ink so that bubbles may be formed therein. The bubbles absorb the forced generated by the pressure elements of the ink jet head which reduces displacement thereof so that the power of the ink ejection is attenuated. This reduction causes missing dots and or smaller dot size. Additionally it is difficult to wet the circumference of an orifice of the nozzle so that the meandering of ink ejection and deformation by the printer printed characters still exists.
The inventors note that surfactants generally roughen the surface of plastic materials. However, the selection of suitable plastics in printing heads using a surfactant-containing ink character has been troublesome.
All the while, each of the above points may have been individually addressed by conventional inks and ink jet printers, the inventors are not aware of any means or device which satisfies each and every one of these characteristics, as explained in detail below
Various attempts have been made to provide an ink jet printer which satisfied the above-mentioned characteristics. But none of these attempts overcame the problems for an ink jet printer with a plastic print head.
For example, Japanese Patent Application Laid Open No. 1-123752, which address points number 1 and 2 above, is directed to a technique of wetting an ink flow pathway from an ink reservoir to a nozzle surface of a recording head in order to obtain uniform wetting of this nozzle surface of the recording head. This technique is accomplished by preventing the generation of bubbles in the ink. More specifically, grooves are arranged symmetrically to the series of nozzle orifices for jetting out the ink there through. The edge of such nozzles are made of Ni, Ti, Si, O.sub.2, Ti, O.sub.2 or the like. Alternatively, the nozzle maybe surfaced-treated by plating, vapor deposition, sputtering or some other coating means. However, the technique discussed in Japanese Patent Application Laid Open No. 1-123752 requires the additional step of forming the head. This additional step increases the unit price of such products. In addition, in accordance with the above-mentioned coating means, it is difficult to completely and uniformly coat the nozzle surface. As a result, the surface of the nozzle edge has a portion which can be wetted with ink and a portion that is not wetted. This configuration causes the jetting direction of the ink drops to meander and, as such, the printed letters or characters have a tendency to be deformed.
Japanese Patent Application Laid Open No. 62-111749 is directed to a printer having a heater-combined hot air blowing unit to promote the drying of the printed ink. This is accomplished by blowing hot air on the just ejected ink. However, such a device is intended to be used in large-scale printers, since this device consumes an inordinate amount of electric power. Additionally, the cost of such devices are high. As such, the device discussed in Japanese Patent Application Laid Open No. 62-111749 is not particularly well suited for the applications discussed above.
Japanese Patent Application Laid Open No. 1-252680 and its European counterpart application 320,223 propose the addition of more than 40 wt. % of a wetting agent and a nonionic acetylene diol surfactant or dioctyl sulfocuccinate surfactant intended for the prevention of the clogging of the print head for the smooth operation of printing on plain paper.
The ink composition comprises a compatible dye, greater than 40 weight % humectant and a surfactant. The surfactant is utilized to facilitate printing on plain paper. In these references the weight % is based on the total ink composition. In this ink composition, the high amounts of humectant are said to be selected to insure that the viscosity of the ink is maintained between about 5.5 and 6.5 centipoise. This reference specifies a dye comprising a liquid mixture of Liquid Blue C.I. 279 and mixed with Direct Red C.I. 236 and Direct Yellow C.I. 107, in the ratio of 3.53/1.35/1.0, and Mobay Special Black SP liquid ink and discusses the use of the following surfactants:
Surfynol GA-1 to 10 weight % PA0 Surfynol 82-10 weight % PA0 Surfynol 465-1 to 10 weight % PA0 Surfynol 485-5 to 10 weight % PA0 Surfynol 136-2 weight %
These documents are silent as to the material employed in the print head. Accordingly, this reference fails to appreciate the problems associated with plastic print heads. Therefore, this reference could not attempt to propose solutions for solving the problems discussed above.
Further, Japanese Patent Publication No. 58-6752 proposes the addition of a tertiary alcohol-ethylene oxide adduct having a chemical structure as follows: ##STR4##
R.sub.5 -R.sub.8 each present alkyl group, p and q each represents an integer of at least one and Y represents an acetylene group.
The addition of such adduct is said to improve the smooth operation of printing with the ink on plain papers including the stability of the ink to resist smearing and running.
Where the techniques of Japanese Patent Application Laid Open No. 1-252680 and Japanese Patent Publication No. 58-6752 are employed, the time for drying the printed ink is said to be shortened by some degree. Thus, printing on plain paper is said to be possible without enlarging the scale of the printer. Additionally, the clogging of the ink jet is said to be prevented as the storage stability and the water-proofness of the ink being used is said to be improved. However, these references do not address the problems of prevent missing dots of a desired matrix of dots and the meandering of ink drops.